Add optional scheme support for push gateway urls (#103)

* Add optional scheme support for gateway urls

* Add requested documentation updates

* Update documentation. Resolve python 2.6.9 bug

* Remove unneeded imports

Author: thekuffs

prometheus_client/exposition.py

@@ -105,6 +105,16 @@ def write_to_textfile(path, registry):
 def push_to_gateway(gateway, job, registry, grouping_key=None, timeout=None):
     '''Push metrics to the given pushgateway.
 
+    `gateway` the url for your push gateway. Either of the form
+              'http://pushgateway.local', or 'pushgateway.local'.
+              Scheme defaults to 'http' if none is provided
+    `job` is the job label to be attached to all pushed metrics
+    `registry` is an instance of CollectorRegistry
+    `grouping_key` please see the pushgateway documentation for details.
+                   Defaults to None
+    `timeout` is how long push will attempt to connect before giving up.
+              Defaults to None
+
     This overwrites all metrics with the same job and grouping_key.
     This uses the PUT HTTP method.'''
     _use_gateway('PUT', gateway, job, registry, grouping_key, timeout)
@@ -113,6 +123,16 @@ def push_to_gateway(gateway, job, registry, grouping_key=None, timeout=None):
 def pushadd_to_gateway(gateway, job, registry, grouping_key=None, timeout=None):
     '''PushAdd metrics to the given pushgateway.
 
+    `gateway` the url for your push gateway. Either of the form
+              'http://pushgateway.local', or 'pushgateway.local'.
+              Scheme defaults to 'http' if none is provided
+    `job` is the job label to be attached to all pushed metrics
+    `registry` is an instance of CollectorRegistry
+    `grouping_key` please see the pushgateway documentation for details.
+                   Defaults to None
+    `timeout` is how long push will attempt to connect before giving up.
+              Defaults to None
+
     This replaces metrics with the same name, job and grouping_key.
     This uses the POST HTTP method.'''
     _use_gateway('POST', gateway, job, registry, grouping_key, timeout)
@@ -121,13 +141,24 @@ def pushadd_to_gateway(gateway, job, registry, grouping_key=None, timeout=None):
 def delete_from_gateway(gateway, job, grouping_key=None, timeout=None):
     '''Delete metrics from the given pushgateway.
 
+    `gateway` the url for your push gateway. Either of the form
+              'http://pushgateway.local', or 'pushgateway.local'.
+              Scheme defaults to 'http' if none is provided
+    `job` is the job label to be attached to all pushed metrics
+    `grouping_key` please see the pushgateway documentation for details.
+                   Defaults to None
+    `timeout` is how long delete will attempt to connect before giving up.
+              Defaults to None
+
     This deletes metrics with the given job and grouping_key.
     This uses the DELETE HTTP method.'''
     _use_gateway('DELETE', gateway, job, None, grouping_key, timeout)
 
 
 def _use_gateway(method, gateway, job, registry, grouping_key, timeout):
-    url = 'http://{0}/metrics/job/{1}'.format(gateway, quote_plus(job))
+    if not (gateway.startswith('http://') or gateway.startswith('https://')):
+        gateway = 'http://{0}'.format(gateway)
+    url = '{0}/metrics/job/{1}'.format(gateway, quote_plus(job))
 
     data = b''
     if method != 'DELETE':